Commits on Apr 1, 2026

1. Spin-then-park receive; free-threaded Python compatibility. (#6) …

   Improvements:
   
   - Added CownCapsule.disown() — abandons a cown's value without
     serializing it and resets ownership to NO_OWNER. Used during worker
     cleanup to safely discard orphan cowns before the owning interpreter
     is destroyed, preventing dangling Python object references.
   - Rewrote receive to use a two-phase spin-then-park strategy for
     single-tag untimed receives. Phase 1 spins for BOC_SPIN_COUNT
     iterations; Phase 2 parks the thread on a per-queue condvar, eliminating
     busy-wait CPU burn. Timed receives and multi-tag receives use
     spin-then-backoff with exponential sleep (1 µs → 1 ms cap).
   - Added platform-abstracted condvar primitives (BOCParkMutex /
     BOCParkCond) with implementations for Windows (SRWLOCK /
     CONDITION_VARIABLE), macOS (pthreads), and Linux (C11 threads).
   - Each BOCQueue now carries a waiters counter, park_mutex, and
     park_cond. Producers signal parked receivers after enqueue;
     drain and set_tags broadcast to wake all parked threads.
   - Replaced the fixed thrd_sleep in send with a sched_yield /
     SwitchToThread, reducing send-side latency.
   - Refactored the monolithic _core_receive into receive_single_tag
     and receive_multi_tag, each with its own backoff/parking logic.
   - Moved the BOC_QUEUE_DISABLED check earlier in get_queue_for_tag
     so callers skip disabled queues instead of returning NULL after
     tag resolution.
   - Added Windows-compatible atomic_load_explicit /
     atomic_fetch_add_explicit / atomic_fetch_sub_explicit macros
     using InterlockedExchangeAdd64.
   - Declared Py_mod_gil = Py_MOD_GIL_NOT_USED in both _core and
     _math C extensions so that importing bocpy on a free-threaded
     Python build (3.13t+) does not re-enable the GIL.
   - Replaced PyDict_GetItem (borrowed reference) with
     PyDict_GetItemRef (strong reference) in BOCRecycleQueue_recycle
     on Python 3.13+, improving forward-compatibility with free-threaded
     builds.
   
   Bug Fixes:
   
   - Fixed a deadlock when the same cown is passed multiple times to @when
     (e.g. @when(c, c)). Duplicate requests for the same cown caused the
     MCS-queue-based two-phase locking to spin-wait on itself. Requests are
     now deduplicated by target cown in Behavior.__init__, with
     compensating resolve_one calls to maintain the behavior count
     invariant.
   
   Tests:
   
   - TestLostWakeStress: single-producer random delays, bursty producer,
     and repeated single-message wake to detect lost-wake races.
   - TestMultiTagBackoff: multi-tag receive correctness — second-tag hit,
     delayed arrival, per-tag FIFO ordering, timeout, and interleaved
     producers.
   - TestTimeoutAccuracy: lower-bound / upper-bound wall-clock checks and
     zero-timeout immediacy.
   - Added tests for duplicate cowns in @when: same cown twice, thrice,
     non-adjacent duplicates, duplicates within a group, and mutation
     aliasing semantics.
   
   CI:
   
   - Added a free-threaded CI job that tests against Python 3.13t and
     3.14t on Linux, with explicit assertions that the GIL remains disabled
     after import.
   
   Signed-off-by: Matthew A Johnson <matjoh@microsoft.com>

   

   matajoh authored Apr 1, 2026
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